Pedestrian tracking and positioning are required for a wide variety of navigation applications, such as search and rescue, military applications, sports and tourism navigation, commercial location-based services, and many more. Several pedestrian navigation aids are known that use low-cost, lightweight devices. There are known hand-held aids, as well as body-mounted aids e.g. devices mounted on head, shoulder, belt, shoe or foot.
There are known pedestrian navigation aids that integrate several sensors and units e.g. Inertial Measurement Unit (IMU, e.g. microelectro-mechanical system (MEMS) including gyroscopes and accelerometers), a pedometer, a magnetometer, Global Positioning System (GPS and like systems), sonar and radar.
An IMU solution typically suffers from errors accumulated due to inertial sensor's drifts: even a small inertial measurement error contributes to high position error, which rapidly grows as a high order polynomial function of time. Thus, pedestrian navigation aids typically include a navigation error corrector, typically implemented as a Kalman filter updating component. Inertial measurements are typically corrected based on local measurements provided by local sensors e.g. the magnetometer, and/or with exterior indications coming from external infrastructure and sources such as a LAN (Local Area Network), radar beacon or GPS. However, a problem arises when such exterior indications or signals are unavailable or not exploitable, e.g. when a GPS signal is blocked or degraded, even occasionally, or when the LAN is unavailable.
The so-called ZUPT (Zero-velocity updates) technique is also used to correct IMU measurements and reduce inertial errors. According to this technique, zero-velocity updates coming from e.g. the inertial sensor are fed into the error corrector that yield a correction input which in turn is provided to a navigation processor and processed with the IMU data. Typically, ZUPT enables correcting parameters such as position, velocity, acceleration, pitch and roll bias, thereby reducing inertial drift errors. Zero-velocity updates are typically provided every time the pedestrian foot (on which the IMU is accommodated) strikes the ground.
The so-called “dead reckoning” (DR or PDR—Pedestrian Dead Reckoning) method is an autonomous method independent of exterior indications, for determining position and other parameters of a pedestrian by calculating the accumulated displacement of the pedestrian from a given starting point. The pedestrian displacement from the known position is calculated based upon some or all of the following measured or calculated parameters: step counting (e.g. using accelerometers), velocity, time, heading (e.g. using gyro signal), and stride length (e.g. using a specific accoustic measuring unit or the known connection (function) between stride length and stride frequency) Typically, PDR position error grows as a function of range rather than of time. PDR parameters are sometimes corrected and calibrated based upon input coming e.g. from a GPS unit.
The following patents and patent applications relate to pedestrian navigation: U.S. Pat. Nos. 4,371,945; 5,583,776; 6,522,266; 6,549,845; 6,826,477, and US Patent Application No. 2002/0143491.
Also relevant to the field of pedestrian navigation are: E. Foxlin, “Pedestrian tracking with shoe-mounted inertial sensors”, IEEE Computer Graphics and applications, November/December 2005, IEEE 0272-1716/05; and S. Gudha, G. Lachapelle and M. E. Cannon, “Integrated GPS/INS systems for pedestrian navigation in a signal degraded environment”, ION GNSS 2006, Fort Worth, 26-29 Sep. 2006; Q. Ladetto, J. van Seeters, S. Sokolowski, Z. Sagan, B. Merminod, “Digital Magnetic Compass and Gyroscope for Dismounted Soldier Position and Navigation”, NATO Research and Technology Agency, Sensors & Electronics Technology Panel; Ross Stirling, Jussi Collin, Ken Fyfe, Gerard Lachapelle, “An Innovative Shoe-Mounted Pedestrian Navigation System”, GNSS 2003, Graz, Austria, April 2003; R. Jirawimut, P. Ptasinski, V. Garaj, F. Cecelja, W. Balachandran, “A Method for Dead Reckoning Parameter Correction in Pedestrian Navigation System”, IEEE Trans. Instrumentation and Measurement, Vol. 52, No. 1, February 2003, pp. 209-215; K. Okuda. S. Yeh, C. Wu, K. Chang, H. Chu, “The GETA Sandals: A Footprint Location Tracking System”, LoCA 2005, Munich, Germany.
GETA sandals provide a navigation system that employs two on-foot modules (wooden sandals) each having two sensor units installed thereon. For example, one module—e.g. left foot sandal—includes two ultrasonic-infrared receivers and the other module—right foot sandal—includes two ultrasonic-infrared transmitters (other sensor configurations are also known). Each time the pedestrian strikes the surface, the transmitters transmit a signal, which is received by the receivers, and signal receipt information is used in performing TOA (Time of Arrival) calculations, thereby facilitating determination of relative displacement vector. GETA sandals and respective navigation methods require substantially full contact of two feet on the surface. However during certain motion types including forward short-step walking, occurrence of such a condition is not always guaranteed. GETA sandals technique provides new position information every second stride. GETA sandals are typically provided with a wooden sole and this typically imposes a burden on the pedestrian.
There is a need in the art for an autonomous pedestrian positioning and navigation device for indoor and outdoor environments which can operate in the occasional or permanent absence of external position indication e.g. GPS or LAN. There is a further need in the art for a navigation device and method suitable for a wide variety of pedestrian motion types. There is a need in the art for an efficient, highly accurate pedestrian navigation device and method. There is a need in the art for a pedestrian navigation device which can provide a high accuracy level with low-class inertial units. There is a need in the art for a compact navigation device.